如何在Shell脚本中匹配然后替换多行

与sed：

sed '/Physical link is/ { :a /MTU:/! { N; ba; }; /Physical link is Up.*MTU: 9000/ { s/\(.*\n\)\s*/<Pass>\1<Pass>/; b; }; s/\(.*\n\)\s*/<Fail>\1<Fail>/; }' filename

那是：

/Physical link is/ {                       # Block start found
  :a
  /MTU:/! {                                # fetch lines until we find the MTU
    N
    ba
  }
  /Physical link is Up.*MTU: 9000/ {       # If link is up and MTU 9000
    s/\(.*\n\)[[:space:]]*/<Pass>\1<Pass>/ # insert Pass markers
    b
                                           # we're done.
  }
  s/\(.*\n\)[[:space:]]*/<Fail>\1<Fail>/   # otherwise insert Fail markers
}

请注意，对于BSD sed，由于b说明，它不能用作单线。在这种情况下，将扩展的代码（不带注释，因为BSD sed容易混淆）放在文件中foo.sed，然后使用sed -f foo.sed filename。我已经\s用它的POSIX等效项（[[:space:]]）替换了其他GNU-ism（）。

要将空格保留在MTU行的开头，请删除\s或[[:space:]]。要将空格放在结果标记之前，请将\s或[[:space:]]放在捕获组内（即\(.*\n\s*\)）。

另请注意：这假设每个接口描述都有一个MTU字段。

或者，您可以尝试以下awk脚本：

awk -v RS='Physical interface:' -F '\n' -v OFS='\n' '{ result = "<Fail>" } /Physical link is Up/ && /MTU: 9000/ { result = "<Pass>" } NR != 1 { for(i = 1; i <= NF; ++i) { if(index($i, "MTU:")) { sub(/^ */, result, $i) } } print result RS $0 }' filename

这会将文件拆分为的记录，Physical interface:并将记录拆分为换行的字段。然后：

{ result = "<Fail>" }                  # result is Fail 
/Physical link is Up/ && /MTU: 9000/ { # unless link is up and MTU 9000
  result = "<Pass>"
}

NR != 1 {                              # the first record is the empty string
                                       # before the first actual record, so
                                       # we remove it.
  for(i = 1; i <= NF; ++i) {           # wade through the fields (lines)
    if(index($i, "MTU:")) {            # find the MTU line
      sub(/^ */, result, $i)           # put the marker there. To keep the
                                       # whitespace, use $i = result $i
                                       # instead, or sub(/^ */, "&" result, $i)
                                       # to keep the spaces before the marker.
    }
  }
  print result RS $0                   # once done, print the whole shebang.
                                       # We have to reinsert the record
                                       # separator because it was removed
                                       # by the splitting.
}

请注意，多字符RS并不严格符合POSIX。不过，最常见的awks（gawk和mawk）都支持它。值得注意的是，BSD awk没有。